Term
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Definition
| Proportion of phenotypic variation due to additive gene effects |
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Definition
| average age of the parents when the offspring are born |
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Definition
| mating based on phenotypic resemblance |
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Definition
| best + best, worst + worst. Increases variation, produces extreme individuals |
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Definition
| best + worst. results in phenotypic uniformity |
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Term
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Definition
| mating of individuals more closely related than under random mating |
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Term
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Definition
| mating of genetically unrelated animals |
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Term
| Inbreeding coefficient (F) |
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Definition
| probability that the two genes at a locus in individual are identical by descent. Half the relationship between parents of the individual |
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Term
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Definition
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Definition
| both alleles from common ancestor |
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Term
| F of full sibs/ parent-child |
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Definition
| F= 1/4, genes in common= 1/2 |
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Term
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Definition
| F= 1/8, genes in common= 1/4 |
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Term
| F of 3rd degree (eg. 1st cousins) |
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Definition
| F= 1/16, genes in common= 1/8 |
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Term
| F of 4th degee (eg. 1st cousins once removed) |
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Definition
| F= 1/32, genes in common= 1/16 |
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Term
| F of 5th degree (eg. 2nd cousins) |
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Definition
| F= 1/64, genes in common= 1/32 |
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Term
| Genetic effects of inbreeding |
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Definition
increases homozygosity (can be without a change in gene frequency)
If there is dominance; aa can be inferior and inbreeding will cause a decrease in performance
Alleles become 'fixed'
decrease in genetic variation |
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Term
| Phenotypic effects of inbreeding |
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Definition
incerased incidence of 'throwbacks'
inbreeding depression
expression of deleterious recessive alleles
prepotency + decrease in phenotypic variation |
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Term
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Definition
| Deciline in performance. The result of non-additive gene action (dominance). Worse in low heritable traits (repoduction, survivability). |
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Term
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Definition
| appears or performs like one of either parent. Most likely to result of individuals homozygous loci contain cheifly dominant alleles |
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Term
| Change in F per generation |
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Definition
1/8Nm + 1/8Nf
Nm & Nf = number of males/females per generation |
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Term
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Definition
1/8nmL^2 + 1/8nfL^2
nm & nf = number of new males/females that enter population each year
L = generation interval
nm = Nm/L |
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Term
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Definition
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Term
| appropriate change in F/yr for production animals |
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Definition
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Term
| appropriate change in F/yr for endanged species |
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Definition
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Term
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Definition
increases uniformity in population
study inheritance pattern of recessive traits
increase hybrid vigour (crossing of 2 divergen inbred lines) |
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Term
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Definition
| constructing pedigrees so that animals are closely related to some 'superior' ancestor |
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Term
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Definition
increase population size
increase the number of males used
bring in outside genetic material
consult with animal breeder |
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Term
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Definition
| unrelated individuals within breed |
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Term
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Definition
| animals from different breeds |
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Term
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Definition
| individuals from different species |
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Term
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Definition
| two inbred lines belonging to the same breed |
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Term
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Definition
| two inbred lines belonging to different breeds |
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Term
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Definition
| inbred males X females of outbred population |
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Term
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Definition
F1 female X one of intial breeds
Maternal heterosis + 50% individual heterosis |
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Term
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Definition
| backcrossing for successive generations to same intial breed |
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Term
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Definition
increases heterozygosity
masks expression of deleterious recessive genes
hybrid vigour/ heterosis = increased mean performance of parents |
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Term
| Advantages of outbreeding |
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Definition
add hybrid vigour
breed complementarity
avoid inbreeding depression
mask effects of deleterious recessive alleles |
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Term
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Definition
| deviation of the average of reciprocal crossbred progeny from the average of the parental breeds |
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Term
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Definition
| hetrosis of fitness traits |
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Term
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Definition
| heterosis of vegetative growth |
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Term
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Definition
| hybrid vigour attributed to heterozygosity of the same outbred individuals upon whom the traits are measured |
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Term
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Definition
| benefits of heterosis in traits accruing to the offspring of the crossbred female, rather than to the female herself. eg. individual milk production in Angus-hereford cows could be reflected as maternal hetrosis in pre-weaning growth in their progeny with Simmental bulls |
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Term
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Definition
| hybrid vigour attributed to the sires, but accrues to the offspring. Eg. cross-bred bulls contribute to increased libido and higher survival rate of crossbred embryos, thereby resulting in more calves being born. |
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Term
| Genetic causes of heterosis |
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Definition
-non-additive gene action-
complete dominance, over dominance, epistasis |
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Term
| Factors affecting heterosis |
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Definition
reciprocal crosses
breeds involved in cross
genetic and envorinmental interaction
differences among traits
breed complementarity |
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Term
| Basic principals of heterosis |
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Definition
max H seen in F1
H proportional to proportion of heterozygosity
H 1/2 in F2 compared to F1
no further decrease in F3; hardy-weinberg equlibrium
F1 backcrossed to parent breed; H 1/2
BC1 backcrossed to breed A there will be further decrease in H
Therefore it is better to keep pure breds for mating rather than backcrossing to parental breeds |
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Term
| Fixed % / specific crossing |
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Definition
| 2 breeds crossed, F1 sold for slaughter or other commercial use. 100% individual heterosis. |
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Term
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Definition
ABxC
50% of breed C + 25% of A&B inheritance
100% IH + maternal H |
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Term
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Definition
ABxCD
25% inheritance of each breed
100% IH + maternal and paternal H |
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Term
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Definition
Cris-crossing:
systemic crossbreeding with 2 breeds
maintaing 2/3 of H seen in F1 generation
Rotational crossing:
4th generation will show 6/7 H of F1 generation
only sires required from pure bred matings, crossbred dams self replacing.
Large variation in breed composiion between generations = marketing and management problems |
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Term
| Composit/synthetic breeds |
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Definition
express less heterosis than specific of sequential
the more breeds used; the more teterosis that will be exhibited |
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Term
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Definition
| Choosing the right breeds to complement each other in a cross allows the best collective performance in all traits affecting the objective of the farming enterprise |
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